1. Field of the Invention
The present invention relates generally to the field of antiviral compounds, particularly compounds that act by inhibiting the ubiquitin ligase activity of a poxvirus p28 protein.
2. Summary of the Related Art
Smallpox is a serious, highly contagious, and frequently a fatal infectious disease for which there is no specific and effective treatment. The primary method of prevention is by vaccination. Two clinical forms of smallpox have been described: variola minor and variola major. The variola major form of smallpox is the most common and severe form. There are four types of variola major smallpox, namely, ordinary (the most frequent); modified (mild and occurring in previously vaccinated persons); flat; and hemorrhagic. Overall, variola major has a case-fatality rate of about 30%.
The most virulent form of smallpox, hemorrhagic smallpox, destroys the linings of the throat, stomach, intestines, rectum, and vagina. It causes black, unclofted blood to ooze from the mouth and other body orifices. Because hemorrhagic smallpox has a much shorter incubation period than other forms of smallpox, it is likely not to be initially recognized as smallpox when first presented to medical care. As such, most victims die prior to a correct diagnosis, often before they are quarantined. Smallpox vaccination provides little protection against hemorrhagic smallpox as hemorrhagic smallpox causes the death of 94% of vaccinated patients and 99% of unvaccinated patients.
Because variola viruses, particularly smallpox, are so fatal, their inclusions in biological weapons or so called “weapons of mass destruction” are currently thought to be a great public threat. Accordingly, there is an urgent need for methods and compositions for treating and preventing infection with variola viruses, especially smallpox.
Despite intense research, the primary treatments and preventions methods for smallpox are either ineffective or impractical in the event of an outbreak from a virulent strain of smallpox. The primary therapeutic tools for the control and eradication of smallpox include a live virus vaccine to prevent disease, and a vaccinia immune globulin (VIG) to treat dissiminated infections. The smallpox vaccine (live vaccinia virus) has many side-effects including adverse reactions, scarring, ocular autoinoculation, increased incidence of myocardial infarction, and dissemination in immunocompromised persons. Cell culture derived vaccines are being developed; however, these vaccines are also live viruses and pose many of the same drawbacks that plague the current vaccine. Accordingly, the public at large, the healthcare community, and the military have been resistant to smallpox vaccinations because the risks of side-effects appear to outweigh the advantages. Further, as discussed above, current vaccination methods are practically ineffective against hemorrhagic smallpox or its derivatives which are forms that would most likely be used in biological weapons.
The existing vaccinia immune globulin products are derived from human donors who have been vaccinated with vaccinia virus (the vaccine for smallpox). As with all human products, VIG must be tested exhaustively for blood borne human pathogens such as human immunodeficiency virus and hepatitis B. Therefore, VIG suffers from several drawbacks including the necessity for using human volunteers, i.e. the use of a live virus as an immunogen which could cause infectious lesions that scar healthy individuals and severe disseminated life-threatening infection in immunocompromised individuals. Despite continuous screening of the donor population to assure consistency which is very expensive, product lots can vary significantly between batches and geographic regions.
Accordingly, the primary treatment for smallpox infection is impractical in most situations. In addition, since vaccinia virus is an ineffective vaccine for hemorrhagic smallpox, it is unlikely vaccinia immune globulin products will be effective against hemorrhagic smallpox.
Research into the biology of smallpox is intensive. For example, the genome of variola virus has been sequenced, and it is about 185 kbp in length and is predicted to contain over 200 proteins. Many of the proteins involved in transcription and DNA replication as well as about 30 proteins that form the core and membrane components of the virus particles have been identified. Other viral proteins have been identified that are thought to interact with host components to facilitate virus dissemination, prevent apoptosis, and attenuate immune responses. However, although well over 10 years have passed since the genome of vaccinia virus was sequenced, the biochemical functions of most viral proteins, in particular, p28, which has been shown to be required for viral pathogenesis, remain elusive. As such, despite great effort, the development of anti-viral assays and the discovery of effective drugs to combat smallpox infection have been letargic.
Accordingly, despite great effort and the continuous threat of a serious hemorrhagic smallpox outbreak, an effective, practical therapy (including prevention and treatment) for smallpox, is currently unavailable. Accordingly, there is a great need for new assays to discover drugs for the treatment of smallpox as well as a great need for new smallpox therapies, particularly those that may be deployed rapidly, safely and in great number. This invention describes compounds, compositions and methods that satisfy these needs and others.